1. Technical Field
The present invention relates in general to an improved method of balancing hard disk drives and, in particular, to an improved method that uses an enhanced balance clip design for use in conjunction with the spindle motor for reducing friction during clip adjustment in the disk pack balance process.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
During manufacturing of the hard disk drive, the sub-assembly of the spindle motor is fabricated and the disks are attached to a hub 11 (FIG. 1) of the spindle motor. In the prior art, the hubs 11 are formed from aluminum, and balance clips 13 are used in the hubs to fine-tune the balance of the hubs 11. As shown in FIG. 1, the balance clips 13 are retained on the hub 11 in balance clip holder features 15, which are typically integrally formed as part of the motor hub 11. Each balance clip 13 has a wire-like body that is formed in a semi-circular shape. Each balance clip 13 also has an integrally formed bent tab 17 on one end that is precisely formed in order to facilitate the balance correction process. Alternatively, the balance clips 13 sometimes comprise split rings.
In either case, an opposite end 19 (see FIG. 5) of each balance clip 13 is cut and forms a relatively sharp edge around the cross-section of the balance clip 13. As a result, movement of the balance clips 13 during the balancing process causes ends 19 to frictionally engage the inner surfaces of the holder features 15. Such contact between ends 19 and hub 11 can be significant and even prevents movement of the balance clip 13. Such contact between ends 19 and hub 11 can also scratch the motor hub groove surface, thereby generating particles and contamination during clip adjustment in the disk pack balancing process. It has been proposed that ends 19 be carefully polished, but such processing adds cost to the product. Although this solution is workable, an improved method that is more cost effective would be even more desirable.